This invention relates to products having a low degree of emissivity, and to methods for producing same, and in particular to low emissivity products which also exhibit a high level of moisture vapor permeability.
As pointed out in U.S. Pat. No. 5,231,814 (“US '814”) and in U.S. Pat. No. 6,251,495 (“US '495”), both of which are incorporated herein in its entirety by reference, and both of which are owned by the assignee of this patent application, roof decking typically is formed of structural wood products, such as plywood or oriented strand board (“OSB”). These structural wood products are attached to the structural members of a house by nails or other fastening means. This roof decking defines the confines of the roof of the house and serves as the substrate for joining the outer protective water-shedding materials, i.e., the tar paper and shingles, which are attached thereto and complete the protective roof assembly.
This roof structure is formed of materials which inherently have minimal thermal insulating and emissivity barrier properties. Therefore, heat transfer through the roof structure from the outdoors to the interior space of, for example, a home, particularly during the summer months, is a problem to homeowner. Either the homeowner undergoes severe discomfort due to elevated temperatures inside the house, or they must pay a high price for installing and operating air conditioning. Prior to the product described in US '814, the insulative solar or heat emitting properties of a structural roof have undergone limited improvements such as by applying insulative materials to the exterior of the roof decking under the outer protective materials.
Excess heat transfer is generated on a daily basis in the summer months, which penetrates into the interstices of building materials such as sheet rock and insulation causing unwanted elevated temperatures within the interior living space. Thus, under conventional home construction conditions, the air temperature in attics and ceilings can be raised to about 140 degrees F. or higher. US '814 addresses certain problems relating to heat transfer. In US '814, a roof structure is fitted with roof decking comprising a substrate of plywood or OSB with a layer of a radiant barrier material adhered thereto. In preferred form of this invention of US '814, the radiant barrier material is subsequently adhered to substrate in a secondary formation sequence. The radiant barrier material comprises a layer of metallic foil such as an aluminum foil material. The foil covered roof decking material is fastened to the rafters in a typical roof structure.
The radiant barrier material used in US '814 includes a plurality of substantially uniformly distributed perforations which are introduced therein prior to applying same to a preformed underlying substrate. When the perforated foil material is applied in a secondary application, this process is conducted under ambient temperature.
The expressed reason for introducing the perforations into the foil material is to permit the passage of moisture between the moisture barrier layer and the roof. In this way, it is thought that a significant portion of excess moisture can be released through the perforations located in the foil material thereby permitting the roof decking to “breathe.” If a significant portion of the excess moisture is not released, unwanted degradation of the substrate can result. Moisture can be present due to, for example, water vapor which enters the house during construction (before the roof is put on), or after construction from roof leaks of various types. Unwanted moisture can also result from the cumulative effect of vapor condensation.
Typically, the decking is placed in position with the foil layer facing inwardly toward the attic of the house. The low emissivity foil faces at least one adjacent air space (the attic) to prevent unwanted heat transfer.
US '495 is also directed to a radiant barrier covered product. The product of US '495 can be formed by adhering a radiant barrier layer to a preformed underlying substrate in a secondary application operation. The underlying substrate can be formed of a variety of materials such wood or wood substrate products, or mineral or polymeric substrate products. The underlying substrate is most preferably formed of a structural wood panel such as OSB, plywood or the like.
A plurality of apertures are then introduced into the radiant barrier material covered product so that these apertures extend substantially completely through the radiant barrier material, substantially completely through any intermediate layer such as paper or the like, as well as substantially completely through the adhesive material, thereby forming substantially completely open moisture vapor flow channels. The apertures also extend through at least one of the outer major surfaces of the underlying substrate. A portion of the radiant barrier material is typically moved into the confines of the apertures, and the radiant barrier material portion is maintained therein without picking a substantial amount of the radiant barrier material portion from within the confines of the apertures.